The present invention relates to a seam arrangement and, more particularly, to a web seam for sheet-metal parts and the process of making the same. The seam is formed by a triple layer web projecting from a surface of the sheet metal part, with the respective layers being formed from a first flange of one sheet metal part and a second flange of another sheet metal part. The second flange is folded over in a U-shape and extends over the first flange with the first flange and a leg of the U-shaped second flange initially joining the sheet metal parts by their being separately connected by spot welding or cementing. The final securement of the flange involves the welding or cementing of both legs of the U-shaped flange to the first flange.
A web seam in an intermediate step in the manufacture of a vehicle roof rain channel is proposed in German Pat. No. 855,235, wherein a curved roof panel with a flange is first tack welded by means of an electric spot welding to a portion of a Z-shaped roof frame of a motor vehicle body. Then by bending a projecting over hanging flange of the roof frame over the the flange of the roof panel, a roof edge is obtained having three times the sheet metal thickness.
In a web seam according to the above-noted German patent, especially with the use of thin-walled sheet metal, if such sheet metal joint is placed under tensile stress at right angles to the web seam, the spot weld connections begin to tear the sheet metal as the seam is pulled open at a relatively low stress since a brittle zone is formed about each spot weld. This is due to the fact that the brittle zone cannot absorb any appreciable load, especially with thin walled metal sheets. Consequently, when the weld seam is subjected to a stress which tends to bend the seam open, the weld spots tear through the sheet metal and "unbuttoned", so to speak.